Thursday, December 18, 2008

Bicycle companies will often put glossy promotional advertisements on their websites while putting forth their sales pitch. Sometimes, they'll even go ahead and even compare a bicycle model from their line to that of a competitor's.

As an example, I was stumped by the frontal view of these two bikes. It was put on Specialized's website in a tutorial pdf called"The Importance of Aerodynamics In Cycling". The idea was to show how 'skinny' the Transition looked from the front compared to Cervelo's P3C.

Fig 1 : Side by side frontal area comparisons

As you can see, there is no rider on the bikes, and no pedals either (hardly the case in the real world).

Specialized makes a big deal out of Cervelo's cables sticking out in the front end. They also critique its flared out seatstays and commend the tucked-in design on same in their bike. If you put things into perspective, these things are probably going to make negligible differences to your power output at constant speed. 70-80% of the drag is from the cyclist, not even shown in this picture, much less from the bike, and still much lesser friction drag from cables. Unless you're fighting for a mere tenths of second or a couple of feet with a your opponent, cable drag is hardly an issue. Even then, remember top pros back in the days had cables sticking out like the antlers on a deer. They did fine, and even broke plenty of records. Armstrong, Lemond and Valverde are just a few specific names.

Anyway, the real interesting thing happens when you flip the Transition sideways. Like in the following image. This isn't on the promotional pdf.

Fig 2 : Exposed cable in side view of the Transition

If Specialized is so keen on discussing exposed cables, perhaps they should have talked about the segment of ugly cable housing peering into the air from the downtube. But they won't. For all they did with ultranarrow stays, integrated brakes and 1 inch steerers on this bike, you'd think they wouldn't overlook this obvious detail.

Getting back to Fig 1, they compare some fat ugly wheelset on the Cervelo p3C with their aerodynamic Roval hub. If Rovals are so good, why aren't they used on the top of the line Transition, as shown in Fig 2 and in the component listing for the bike on their website? Apparently, Rovals aren't good for the best bike in the time trial lineup and they shamelessly stick with Zipps.

Now lets view the P3C from the side.

Fig 3 : P3C Side View

Compare and contrast this clean look with the bent proportions of Fig 2. Which is better? Since Specialized makes a big deal out of frontal area, perhaps they would know that sloping top tubes actually increase frontal area and is generally a bad profile for aerodynamics. But they won't tell you this either.

Don't get me wrong. I have no overwhelming affections for Cervelo. But this was just a poor show from Specialized against one of the best time trial designs in the market. Cervelo created a benchmark with the P3C, and I'm sure you'll agree with me.

So here's the bottomline : A company will only highlight some couple of points of a product that are favorable to their proposal. These will generally look good. If they highlight bad points, then whats the point in selling it in the first place, right?

Well, turns out that this is really a limited view for the audience who see it. For customers and interested parties pouring over advertisements and promotional product materials such as these, it pays to do some good critical reading and cross checking information before falling too easily.

As for Specialized, it seems like they should really study some aerodynamics themselves first before writing "tutorials".

In that first picture, too, the Specialized site says something about the Cervelo's flared seatstays...but on the Specialized bike, what are those squarish flares back by the rear axle? Aren't those flared seatstays, too? They look like a couple of potential "air brakes"!

You're right, of course -- SO MUCH of the aero advantage comes from the rider, his/her positioning and equipment (skinsuit, helmet, etc.). But those facts don't sell a sexy bike or make for interesting marketing hyperbole!

Anon @ 8:18 If Specliazed wanted to do a good comparison, they would produce real data. Air may not move in predictable ways, which is something Specialized does not realize. This poor comparison is nothing short of their way to undermine Cervelo's design.

Apart from aerodynamics, I see sloping top tubes as more of an advantage. More fit opions, and lower center of gravity. It would be interesting to see how much this kind of steep slope would affect air flow , perhaps a flow visualization would be apt.

I love that front hub whose entire aero advantage is gained from bringing the flanges in, thus weakening the wheel. how many other parts of a bike could be made slipperier if only we were willing to sacrifice that oh-so-overated "strength and durability?"

Specialized did produce the real air data. It beat the P3C by 9% at 0 angle of attack. It's rather funny that this real data is in the same report that this post is criticizing... I'll agree with Anonymous @8:18, I have seen air do many funny things in the wind tunnel.